The fluidization behaviors of various nanometer and micron particles, including SiO2, TiO2, and cornstarch particles with primary particle sizes of 5 nm-10.69 mu m, were investigated in a fluidized bed with inside diameter 56 mm under different sound pressure levels and sound frequencies. It has been demonstrated that the relatively uniform ultrafine particle agglomerates reach homogeneous fluidization with sound assistance at low sound frequencies due to the sound field disrupting large size agglomerates. Furthermore, slugging and channeling of the bed was eliminated, accompanied by negligible elutriation. For each of the nanometer and micron particles examined, the minimum fluidization velocity decreased with increasing sound frequency, and then increased with sound frequency at a given sound pressure level. There is a minimum value in the curve of minimum fluidization velocity versus sound frequency, the critical sound frequency, at which the bed fluidized smoothly. Varying the sound pressure level can significantly improve the fluidization quality of the bed.